An agricultural baler is a trailed machine (PTM—pulled type machine) used in agriculture for the purpose of creating bales of (typically) straw or other biomass such as hay, silage or similar crop material produced during a harvesting or mowing operation.
Various designs of balers have been proposed in the prior art. A common characteristic of virtually all balers is that they are towed behind agricultural vehicles such as tractors. A baler includes an infeed via which biomass is ingested into the interior of the baler and compressed or otherwise treated to form bales. The completed bales are tied with twine to make them rigid and self-supporting and are ejected via a discharge chute typically at the rear of the baler machine so as to fall or be placed on the ground behind the tractor/baler combination as its moves forwardly along a harvested field.
In the 1970's and 1980's, so-called “round” balers were developed. These produce large cylindrical bales. Although many round balers are still sold annually and many more remain in use, in many areas their popularity has been usurped by “rectangular” or “square” balers. Such balers produce cuboidal bales that have a number of advantages over “round” bales.
The handling of rectangular bales is more convenient and is safer. Additionally as a result of the cuboidal shapes of rectangular bales it is relatively easy to transport them and stack them for temporary or long term storage in stable structures either in fields or in farmyards. Rectangular bales can be produced with a high density. When used, rectangular bales are also easily distributed as they are formed from a number of slices.
A significant advantage of rectangular balers over round balers is that it is possible to adjust the characteristics of a rectangular bale in some cases while the bale is being formed.
This is important because straw or other baled biomass is an economically valuable crop. Very often the value of baled biomass is assessed on the basis of the weight of each bale produced by the operation of the baler. It can be very important to control the density of the baled biomass in order to assure that the bale weights are substantially constant during passage of a baler from part of a field to another. Variations, however, in the characteristics (especially the moisture) of the baled biomass ingested from place to place into the baler may mean that there is a frequent or even constant need to adjust bale density during baling operations in order to meet the objective of consistent bale mass.
In a rectangular baler it is possible to adjust the bale density, as the baler includes a substantially cuboidal bale-forming chamber. It is known in the art to construct the bale-forming chamber with one or more moveable side walls. The positions of the side walls can be adjusted so as to alter the volume of the bale-forming chamber and thereby squeeze the bale during its formation to a greater or lesser degree. If, as is commonplace in a baler, each charge of ingested biomass is substantially of constant volume, causing a reduction in the volume of the bale-forming chamber in this way leads to the creation of higher density bales, and vice versa. This, in turn, provides an ability to control the densities of the formed bales.
In more detail, each charge introduced into the bale-forming chamber is, at the point of introduction, uncompressed or compressed to a relatively low level. It is moved along the bale-forming chamber by longitudinal strokes of a piston that reciprocates under the action of an attached arm that in turn is driven by a bell crank secured to a rotating member. Each stroke of the piston therefore compresses an amount of biomass against the biomass already available in the bale-forming chamber. In consequence, the density of the formed bale increases if the volume into which the biomass is swept is reduced as a result of adjustments of the positions of the sidewalls of the chamber at locations “downstream” of the furthest point reached by the piston during its motion.
The dimensions of rectangular bales, however, are substantially fixed, firstly because of the cross-sectional dimensions of the bale-forming chamber and secondly because the baler forms the biomass into identical bale lengths that are ejected via the discharge as substantially identical, individual bales.
An example of an adjustable bale-forming chamber sidewall is shown in U.S. Pat. No. 4,037,528. This disclosure describes sidewalls that are moveable under the influence of cam-like arms that are caused to rotate by attached hydraulic rams. The arrangement defines a pair of four-bar linkages each including one of the sidewalls. Operation of the associated ram therefore causes the sidewall to move inwardly or outwardly, relative to the interior of the bale-forming chamber, in an even fashion causing uniform alteration of the chamber volume over a portion of its length.
A more modern form of bale density adjustment that is suitable for inclusion in a rectangular baler is disclosed in EP0655190.
The ability to adjust the density of bales is likely to be of most use if the baler can be operated in a feedback control mode for the purpose of assessing whether the actual bale density achieved matches a target density value.
U.S. Pat. No. 2,796,825 discloses a hydraulic control system for a rectangular baler, wherein the baler can be operated in a target weight control mode. In the rectangular baler of U.S. Pat. No. 2,796,825, the output value of a weighing platform in the discharge chute is generated as an hydraulic pulse, which is used as an input command to a piston that adjusts the positions of sidewalls in a bale-forming chamber. In the baler of U.S. Pat. No. 2,796,285 therefore bale mass measurements are used to adjust bale density.
A significant drawback of the arrangement disclosed in U.S. Pat. No. 2,796,825, however, is that the weighing platform disclosed therein only generates a signal when a completed bale is stationary on it. Since it takes at least 30 seconds, and most often more, up to 120 seconds, to form a bale in even a modestly-sized rectangular baler the response frequency of the system disclosed in U.S. Pat. No. 2,796,825 is no better than 0.033 Hz and it typically would be significantly slower than this.
A tractor towing a baler across a harvested field, however, may attain a speed of perhaps 15 km/h when travelling over windrows. During the time required to form a single bale, therefore, the tractor/baler combination will travel at least 200 meters. The characteristics of e.g. cut straw lying in a field on the other hand may vary significantly over a distance of one meter or less. The bale weight signals generated using the apparatus of U.S. Pat. No. 2,796,825, being updated say once every 50 seconds, are relatively unlikely to be capable of taking account of such variations.
Another way to control the density of bales created by a rectangular baler is disclosed in co-pending application BE2010/0081. The baler has a bale-forming chamber from which part of the dimensions are adjustable under influence of at least one actuator coupled to a hydraulic circuit. The baler furthermore comprises a controller which allows to operate the baler in a feed-back density control mode. The control mode of the described baler comprises three nested control loops, wherein the loop frequency of the middle control loop is higher than the loop frequency of the outermost control loop and lower than the loop frequency of the innermost control loop. The innermost control loop is a target pressure loop which compares a target pressure value to a measured value of the pressure in the hydraulic circuit of the baler. The middle loop is a target force loop which compares a target force value to a measured value of the force applied by the baler piston. The outermost loop is a target weight loop which compares a target weight value of an individual bale to the measured weight of a finished bale. The described control system is a high-frequency control system which increases the precision of the weight of the resulting bale and automatically takes account of biomass parameter variations during bale formation.
Several other ways to control the density of bales created by a rectangular baler are known in the prior art. Often, the baler is operational in several control modes, for example in a target weight control mode and a target pressure control mode. In the known prior-art methods, the operator, however, is only able to select one of the control modes, while depending on the circumstances neither of them alone might be ideal.